The metabolism of benzo(a)pyrene (B(a)P) and other polynuclear aromatic hydrocarbon carcinogens to highly reactive diol epoxide derivatives is thought to be an important step in the process of carcinogenesis. Diol epoxides bind covalently to DNA both in vitro and in vivo, forming adducts which differ in chemical structure and in their conformation in native DNA. As a result of these differences in structure, different adducts have varying biological effects. The relationship between DNA adduct conformation and biological effects will be studied in a strain of Chinese hamster ovary cells (CHO) in which mutation at two genetic loci and expression of a transfected viral gene (thymidine kinase) can be measured. Using a series of diol epoxides derived from B(a)P, which span the range of known DNA adduct conformations, the rates of formation and removal of DNA adducts in CHO cells will be determined and related to four biological endpoints: cytotoxicity, mutation at the hprt locus, mutation at the oua locus, and expression of an exogenous gene modified in vitro with the diol epoxides and transfected into the cells. These experiments will be carried out in DNA repair-proficient CHO cells and in several recently derived, mutant cell lines which are deficient in repair of DNA damage. This will allow the determination of biological potencies on a per adduct formed basis and the comparison of rates of repair of different DNA-adducts and the effectiveness of the repair system in ameliorating biological damage. The combined use of cells which differ only in their ability to repair DNA-damage and of the DNA-mediated gene transfer assay system will allow the separation of effects due to DNA damage from those due to covalent binding to other classes of macromolecules.